This invention relates to ink jet printing systems, and more particularly to techniques for providing accurate datums for a print cartridge.
Ink-jet printers are in widespread use today for printing functions in personal computers, graphics plotters, facsimile machines and other applications. Such printers typically include replaceable or semipermanent print cartridges which hold a supply of ink and carry the ink-jet printhead. The cartridge typically is secured into a printer carriage which supports one or a plurality of cartridges above the print medium, and traverses the medium in a direction transverse to the direction of medium travel through the printer. Electrical connections are made to the printhead by flexible wiring circuits attached to the outside of the cartridge. In a typical cartridge, the flexible wiring circuit is called a TAB head assembly, or THA, and the printhead is fabricated on the TAB circuit and integrated into the THA. The carriage receptacle has a corresponding electrical circuit with exposed contact pads which contact cartridge interconnect pads when the cartridge is mounted in the carriage. Each printhead includes a number of tiny nozzles defined in a substrate and nozzle plate structure which are selectively fired by electrical signals applied to the interconnect pads to eject droplets of ink in a controlled fashion onto the print medium. The cartridge may be connectable to auxiliary supplies of ink for replenishing the internal supply held in the cartridge.
In order to achieve accurate printing quality, each removable cartridge includes datum surfaces which engage against corresponding carriage surfaces to precisely locate the cartridge when inserted into the carriage. In this manner, when a cartridge ink supply is exhausted, the cartridge may be replaced with a fresh cartridge, and the printhead of the new cartridge will be precisely located relative to the carriage. The printer carriage receptacle and the cartridge are therefore designed together, so that the cartridge fits accurately within the carriage receptacle, the respective circuit pads and datum surfaces match up, and the cartridge can be removed and replaced with a fresh cartridge as needed.
For a typical inkjet printer, the media is loaded into the printer, and is advanced along a media path to a print area. A swath-type printer includes a carriage mounted for scanning movement along a swath axis, transverse to the media path at the print area. Hereafter, the media path is known as the X-axis, the scanning or swath axis is the Y-axis, and the Z-axis is mutually orthogonal to the X-axis and the Y-axis. For color printing, the carriage holds a plurality of ink-jet printheads, each for printing a different color ink, typically black, cyan, magenta and yellow. The printer can include a media drive mechanism for moving the media along the media path, and a carriage drive mechanism for scanning the carriage along the scan axis. The printer controller issues print control signals to cause the printheads to eject droplets of ink in a controlled manner to form a desired image or plot on the medium.
Inkjet printing is based on accurate ballistic delivery of small ink droplets to exact locations onto the paper or other media. Typically the droplet placement occurs onto a grid of different resolutions, most common grids being 300xc3x97300 dpi or 600xc3x97600 dpi, although other solutions are continuously being considered. One key factor for sharp and high quality images stems from the accuracy of the droplet placement.
Improvement of droplet position error during printing has been achieved by controlling drop trajectory through control of nozzle geometry, specifically controlling the angle of the nozzle axis relative to the media surface. Normal manufacturing variability requires that some variability in drop trajectory will always exist, and therefore the droplet position error improvements that can be realized by controlling drop trajectory alone are limited.
A technique for fabricating datum surfaces on a print cartridge body is described, and includes fixing the print cartridge in a tooling fixture, performing a position measurement on the fixed print cartridge to obtain position measurement data, and using the position measurement data to determine precision datum surface locations on the cartridge body in relation to the tooling fixture, conducting machining operations at one or more datum locations on the body to fabricate precision datum surfaces on the body. The datum surfaces are spaced from the nozzle array surface by a respective distance along a first direction, and determine a nozzle-array-to-print-media spacing during printing operations. The fabrication of the datum surfaces using the position measurement data provides accurate location of the datum surfaces relative to the nozzle array substrate in a direction transverse to the substrate.